This invention relates to a level sensing device for dielectric liquids.
In particular, this invention relates to a device for sensing the presence of lubricating oil at a predetermined level in a collection tank disposed in a motor vehicle engine.
The lubricating oil level in a vehicle engine is generally checked by inserting a suitable rod into the tank and observing whether the oil wets the rod between two reference notches which indicate a minimum and a maximum level respectively.
In order to allow the oil to be checked without approaching the engine, sensor devices are at present used which automatically supply an electrical signal which depends on the presence of the oil at a predetermined level. These sensor devices are divided substantially into a first type for insertion into the tank through a bore already provided for introducing the rod, and a second type for housing at a predetermined level in a lateral wall of the tank.
In general, the sensor devices of the first type are rather bulky and consequently the said bore has to be enlarged in order to house them. In the case of devices of the second type, in addition to providing a transverse bore in the lateral tank wall, it is also necessary to use a bush or other seal means as the oil level must always exceed the level at which the device is located. Consequently, the use of such sensor devices is expensive because the labour cost for installing the device has to be added to its actual cost.
Furthermore, as the oil level can be checked either with the engine cold or hot, i.e. over a temperature range which can exceed from -40.degree. C. to +150.degree. C., it has been found that the measurements provided by present day devices are often influenced by the engine temperature.